Have you taken chrome plate into account?
According to TEW parts look up, 530069605 is original # for 42cc LE piston, now been superceeded to 530071408...this # is what I got for my 2150 P/C replacement. since I bought the pair new, I lucked out. Runs like a top.
However I'm very new to all this and don't know the full effect of mix and matching chrome vs plain aluminum components. I can remember a thread with PN quoted with size differences for some engines with 5 thou difference for the same size engine with chrome.
I'm not afraid to try things so I will be boring out my dead 3400 cylinder and putting a chrome 3.7 piston in it...or even a 3.9, but I will have to research what will work and if I have to port the cylinder and if the carb will flow enough.